The treatment and disposal of spent industrial process waste waters, particularly acid-containing waste waters, has been a long standing problem in many industries. Acid-containing waste waters, also known as spent acid streams, are by-products of numerous manufacturing and refining processes. Increasingly higher disposal costs and numerous environmental issues connected with "hazardous" waste disposal have accentuated the need to treat acid-containing waste waters. For example, many local municipalities are enacting measures designed to encourage industrial waste water generators to seek alternative methods of treatment that do not rely on traditional neutralization and landfill practices. The pressure for new treatment methods is also enhanced by the diminishing amounts of landfill space capable of handling spent industrial waste water, and acid-containing waste water in particular.
Sulfuric acid is, by far, one of the most widely used chemicals in industrial chemistry. Annually, sulfuric acid production in the United States exceeds 48 million tons. Sulfuric acid is used, for example, in etching processes, in electroplating processes, in battery acids, in fertilizers, in catalysts such as hydrocarbon refining alkylation, as well as a reagent for chemical synthesis. From such uses, one-third, or up to 16 million tons per year of sulfuric acid must be disposed of as an acid-containing waste. Current disposal methods are inadequate to meet this need, involve costly technologies, and/or generates additional waste to be disposed.
An example of a particular industry in need of recovering sulfuric acid from a waste product is the petroleum industry. Worldwide economic development has resulted in increasing demand for petroleum energy products, especially high-octane gasoline. A class of petroleum-derived compounds known to have particularly high octane ratings are branched paraffins, having from about 6 to 12 carbon atoms. Unfortunately, the amount of naturally occurring C.sub.6-12 paraffins in crude petroleum is limited and is insufficient to meet the increasing demand for high octane blends. Accordingly the petroleum industry has relied upon sulfuric acid catalysts to aid in synthesizing branched paraffins from existing materials to supplement the naturally existing supply of such high-octane materials. The sulfuric acid catalysts aid in the alkylation of short-chain isoparaffins with short-chain olefins, derived from various refinery processes. A more detailed discussion of sulfuric acid alkylation is provided in L. F. Albright et al., "Alkylation of Isobutane with C.sub.4 Olefins," 27 Ind. Eng. Chem. Res., 381-397, (1988), herein incorporated by reference in its entirety. Unfortunately, as described by L. F. Albright et al., a large volume of sulfuric acid catalyst is necessary to catalyze the alkylation process as the sulfuric acid employed should be fresh or relatively pure sulfuric acid. Consequently, the hydrocarbon alkylation process produces large quantities of a waste product containing sulfuric acid for which the disposal costs continue to rise.
Neutralization is the most popular method of waste sulfuric acid solutions. To neutralize sulfuric acid, a variety of bases are added to a sulfuric acid wastewater stream until the stream has been totally neutralized. A considerable drawback to this process is that for every ton of acid, four tons of base are generally required. Thus, for every ton of sulfuric acid, neutralization disposal techniques produce five tons of waste generally requiring landfill disposal.
Reverse osmosis has also been used to treat or dispose of sulfuric acid. Reverse osmosis forces waste sulfuric acid through costly filtration systems until the acid content of the stream is reduced to a level where the remaining stream can be disposed of by conventional means. This requires an expensive filtration system which is generally difficult to build and maintain. Moreover, current reverse osmosis filtration systems are only effective for treating small volume streams.
Evaporation represents another possible disposal method to treat sulfuric acid-containing wastes. However, to dissipate or remove water from an aqueous sulfuric acid solution requires significant energy input and, therefore, carries a high cost.
Incineration may be also used to dispose of waste sulfuric acid. Like evaporation, incineration is not expensive but may lead to the creation of acid rain. The possibility of acid rain makes incineration environmentally unacceptable.
As a result of the limitations in current disposal methods, there exists a need for a cost effective and environmentally prudent method to treat and/or dispose of waste sulfuric acid. A further need exists to reduce the amount of sulfuric acid-containing waste requiring ultimate disposal in a landfill. A preferable answer to this need would be to recycle spent sulfuric acid streams such that they may be reused. Recycling sulfuric acid would also answer and reduce the need for landfill disposal. While many sulfuric acid recycling processes have been proposed in the past (see, e.g., U.S. Pat. Nos. 4,163,047, 4,954,322, 5,275,701 and 5,228,885) to date, there has been no commercially feasible process to recycle spent sulfuric acid streams.